The optical conductivity sigma(omega) and the spectral weight W(T) of two superconducting cuprates at optimum doping, Bi(2)Sr(2-x)La(x)CuO(6) and Bi(2)Sr(2)CaCu(2)O(8), have been first measured up to 500 K. Above 300 K, W(T) deviates from the usual T(2) behavior in both compounds, even though sigma(omega -> 0) remains larger than the Ioffe-Regel limit. The deviation is surprisingly well described by the T(4) term of the Sommerfeld expansion, but its coefficients are enhanced by strong correlation, as shown by the good agreement with dynamical mean field calculations. RI Capone, Massimo/A-7762-2008